Existing engine throttling systems typically employ a throttle shaft rotatable between an adjustable idle position and an adjustable full throttle position. Such rotatable throttle shafts are normally arranged to control fuel flow through variable alignment ports. The degree of alignment of the ports is determined by the rotational position of the shaft. To permit adjustments in the idle and full throttle fuel flows, the throttle shaft is provided with a stop engaging element adapted to engage threaded adjustment screws or stops at idle and the full throttle position of the shaft, respectively. The length of these screws is adjusted as required to limit the travel of the throttle shaft stop engaging element. When the throttle shaft stop engaging element contacts the idle screw, the throttle shaft has been rotated so that only the fuel required to maintain the engine at idle speed will be directed through the throttle shaft ports. When the throttle shaft stop engaging element contacts the full throttle screw, the throttle shaft has been rotated so that a maximum amount of fuel will be directed through the throttle shaft.
Movement of the throttle shaft and throttle shaft stop engaging element between the idle and full throttle positions is usually accomplished by a throttle lever operatively connected to both an operator-actuated throttle control and one or more return springs. Advancement of the throttle control by a human operator causes the throttle lever to move the throttle shaft so that the stop engaging element travels toward the full throttle position. The full throttle position in which the throttle shaft stop contacts the full throttle screw should be reached when the throttle control is completely advanced. Release or retraction of the throttle control causes the vehicle return spring to move the throttle lever and, thus, the throttle shaft and stop element to the idle position so that the throttle shaft stop element is stopped by contact with the idle adjustment screw. Return of the throttle shaft to the preset idle position, therefore, is dependent upon the proper functioning of the throttle lever mounting bolt assembly. If the throttle lever mounting bolt assembly breaks or becomes loose, the throttle shaft may not return to the preset idle position. Should this occur, the throttle shaft will remain in an advanced position, and the throttle return spring will not be able to move the throttle shaft to the idle position since the throttle lever has lost its grip with the throttle shaft.
U.S. Pat. Nos. 3,704,635 to Eshelman and 3,760,786 to Marsh both disclose safety springs which, in the event of a failure of the return spring, return the throttle to the idle position. However, the throttle return systems described in these patents are designed to function only in the event of a return spring failure and require the throttle levers to remain intact for proper functioning. There is no provision for returning the throttle shaft to an idle position in the event of breakage or failure of the throttle lever itself.
Mechanisms which shut down engine operation by shutting off the delivery of fuel to the engine are known in the prior art. U.S. Pat. No. 4,512,306 to Brasseur et al., for example, discloses a spring loaded mechanism for returning a fuel amount control rod to a zero delivery position including a lockable stop which is locked in a maximum fuel position. When an inadmissible engine operating condition, for example an overspeed, is detected, the stop is unlocked. A shut down spring assists the stop to return the control rod to the zero delivery position, thereby shutting down the engine. There is no suggestion in this patent, however, either that this mechanism may be employed to move a throttle shaft to the idle position or that the maximum stop may include an additional mechanism to return the throttle shaft to the idle position if the throttle lever becomes inoperative. The stop disclosed in this reference is held in a locked position and, therefore, requires separate control circuits, first to detect the inadmissible engine condition and then to unlock the stop. Not only is this mechanism complex, but it requires a separate control for cutting off fuel flow.
U.S. Pat. No. 3,572,304 to Becker et al. discloses an engine shut off mechanism having a shut off lever which turns a sleeve, thereby rotating another lever into contact with a plate to thrust the plate against the opposition of a spring to move the control rod to a shut off position. However, this mechanism relies on the action of at least two levers to function and not only is there no suggestion that the mechanism would continue to function if the levers were broken or damaged, but there is also no suggestion that it may be employed to return a throttle shaft to the idle position in the event of an unacceptable engine operating condition such as a broken throttle lever.
The prior art, therefore, has failed to provide a simple, self-contained throttle return safety device which will automatically move the fuel pump throttle shaft from a full fuel to an idle position upon the failure of the throttle lever mounting bolt assembly.